This invention relates to a method for recovering a wafer and a wafer and its fabrication method, and more particularly to a method for recovering a control wafer/dummy wafer and a control wafer and a dummy wafer and their fabrication method.
In the semiconductor industry, in order to enhance the process quality, a control wafer (monitor wafer) is used for monitoring the process stability of equipments, such as the deposition rate or the number of particles. There is another kind of wafer called a “dummy wafer.” A dummy wafer is used for maintaining the stability of a single-batch process. It is usually placed in a position where no product wafer or productive wafer is inside, so as to keep a field stable in reactors or to achieve other purposes for the process stability.
Because these kinds of nonproductive wafers are not used for manufacturing products, in general, manufacturers will recover the control wafer or the dummy wafer for reuse.
A control wafer is a bare wafer without deposits thereon before being used in a deposition process; however, the control wafer has a deposition layer on the silicon surface after used. The deposition layer is sometimes a pure substance or sometimes a compound (or a mixture).
Chemicals, such as etching solutions, are used for removing the deposition layer of a compound (or a mixture), whose components are more complicated. For example, the etching solution containing phosphoric acid, nitric acid and acetic acid is used for removing the AiSiCu alloy (see M. Sze ed., VLSI Technology, 2nd ed., 1988, McGraw-Hill Book Company, U.S.A., p. 398.); however, using this etching solution to recover control wafers and dummy wafers has the following disadvantage: a user must make a great effort to adjust the composition, the concentration and the temperature of the etching solution when the efficacy of removing the deposition layer is not so good.
Therefore, it is important to develop a new wafer-recovering method where, after a wafer is used as a control wafer or a dummy wafer, a less-component etching solution can be used to remove the deposition layer.